

var Matrix4 = function(opt_src) {
    var i, s, d;
    if (opt_src && typeof opt_src === 'object' && opt_src.hasOwnProperty('elements')) {
        s = opt_src.elements;
        d = new Float32Array(16);
        for (i = 0; i < 16; ++i) {
            d[i] = s[i];
        }
        this.elements = d;
    } else {
        this.elements = new Float32Array([1,0,0,0, 0,1,0,0, 0,0,1,0, 0,0,0,1]);
    }
};

/**
 * Set the identity matrix.
 * @return this
 */
Matrix4.prototype.setIdentity = function() {
    var e = this.elements;
    e[0] = 1;   e[4] = 0;   e[8]  = 0;   e[12] = 0;
    e[1] = 0;   e[5] = 1;   e[9]  = 0;   e[13] = 0;
    e[2] = 0;   e[6] = 0;   e[10] = 1;   e[14] = 0;
    e[3] = 0;   e[7] = 0;   e[11] = 0;   e[15] = 1;
    return this;
};

/**
 * Copy matrix.
 * @param src source matrix
 * @return this
 */
Matrix4.prototype.set = function(src) {
    var i, s, d;

    s = src.elements;
    d = this.elements;

    if (s === d) {
        return;
    }

    for (i = 0; i < 16; ++i) {
        d[i] = s[i];
    }

    return this;
};

/**
 * Multiply the matrix from the right.
 * @param other The multiply matrix
 * @return this
 */
Matrix4.prototype.concat = function(other) {
    var i, e, a, b, ai0, ai1, ai2, ai3;

    // Calculate e = a * b
    e = this.elements;
    a = this.elements;
    b = other.elements;

    // If e equals b, copy b to temporary matrix.
    if (e === b) {
        b = new Float32Array(16);
        for (i = 0; i < 16; ++i) {
            b[i] = e[i];
        }
    }

    for (i = 0; i < 4; i++) {
        ai0=a[i];  ai1=a[i+4];  ai2=a[i+8];  ai3=a[i+12];
        e[i]    = ai0 * b[0]  + ai1 * b[1]  + ai2 * b[2]  + ai3 * b[3];
        e[i+4]  = ai0 * b[4]  + ai1 * b[5]  + ai2 * b[6]  + ai3 * b[7];
        e[i+8]  = ai0 * b[8]  + ai1 * b[9]  + ai2 * b[10] + ai3 * b[11];
        e[i+12] = ai0 * b[12] + ai1 * b[13] + ai2 * b[14] + ai3 * b[15];
    }

    return this;
};
Matrix4.prototype.multiply = Matrix4.prototype.concat;

/**
 * Multiply the three-dimensional vector.
 * @param pos  The multiply vector
 * @return The result of multiplication(Float32Array)
 */
Matrix4.prototype.multiplyVector3 = function(pos) {
    var e = this.elements;
    var p = pos.elements;
    var v = new Vector3();
    var result = v.elements;

    result[0] = p[0] * e[0] + p[1] * e[4] + p[2] * e[ 8] + e[11];
    result[1] = p[0] * e[1] + p[1] * e[5] + p[2] * e[ 9] + e[12];
    result[2] = p[0] * e[2] + p[1] * e[6] + p[2] * e[10] + e[13];

    return v;
};

/**
 * Multiply the four-dimensional vector.
 * @param pos  The multiply vector
 * @return The result of multiplication(Float32Array)
 */
Matrix4.prototype.multiplyVector4 = function(pos) {
    var e = this.elements;
    var p = pos.elements;
    var v = new Vector4();
    var result = v.elements;

    result[0] = p[0] * e[0] + p[1] * e[4] + p[2] * e[ 8] + p[3] * e[12];
    result[1] = p[0] * e[1] + p[1] * e[5] + p[2] * e[ 9] + p[3] * e[13];
    result[2] = p[0] * e[2] + p[1] * e[6] + p[2] * e[10] + p[3] * e[14];
    result[3] = p[0] * e[3] + p[1] * e[7] + p[2] * e[11] + p[3] * e[15];

    return v;
};

/**
 * Transpose the matrix.
 * @return this
 */
Matrix4.prototype.transpose = function() {
    var e, t;

    e = this.elements;

    t = e[ 1];  e[ 1] = e[ 4];  e[ 4] = t;
    t = e[ 2];  e[ 2] = e[ 8];  e[ 8] = t;
    t = e[ 3];  e[ 3] = e[12];  e[12] = t;
    t = e[ 6];  e[ 6] = e[ 9];  e[ 9] = t;
    t = e[ 7];  e[ 7] = e[13];  e[13] = t;
    t = e[11];  e[11] = e[14];  e[14] = t;

    return this;
};

/**
 * Calculate the inverse matrix of specified matrix, and set to this.
 * @param other The source matrix
 * @return this
 */
Matrix4.prototype.setInverseOf = function(other) {
    var i, s, d, inv, det;

    s = other.elements;
    d = this.elements;
    inv = new Float32Array(16);

    inv[0]  =   s[5]*s[10]*s[15] - s[5] *s[11]*s[14] - s[9] *s[6]*s[15]
        + s[9]*s[7] *s[14] + s[13]*s[6] *s[11] - s[13]*s[7]*s[10];
    inv[4]  = - s[4]*s[10]*s[15] + s[4] *s[11]*s[14] + s[8] *s[6]*s[15]
        - s[8]*s[7] *s[14] - s[12]*s[6] *s[11] + s[12]*s[7]*s[10];
    inv[8]  =   s[4]*s[9] *s[15] - s[4] *s[11]*s[13] - s[8] *s[5]*s[15]
        + s[8]*s[7] *s[13] + s[12]*s[5] *s[11] - s[12]*s[7]*s[9];
    inv[12] = - s[4]*s[9] *s[14] + s[4] *s[10]*s[13] + s[8] *s[5]*s[14]
        - s[8]*s[6] *s[13] - s[12]*s[5] *s[10] + s[12]*s[6]*s[9];

    inv[1]  = - s[1]*s[10]*s[15] + s[1] *s[11]*s[14] + s[9] *s[2]*s[15]
        - s[9]*s[3] *s[14] - s[13]*s[2] *s[11] + s[13]*s[3]*s[10];
    inv[5]  =   s[0]*s[10]*s[15] - s[0] *s[11]*s[14] - s[8] *s[2]*s[15]
        + s[8]*s[3] *s[14] + s[12]*s[2] *s[11] - s[12]*s[3]*s[10];
    inv[9]  = - s[0]*s[9] *s[15] + s[0] *s[11]*s[13] + s[8] *s[1]*s[15]
        - s[8]*s[3] *s[13] - s[12]*s[1] *s[11] + s[12]*s[3]*s[9];
    inv[13] =   s[0]*s[9] *s[14] - s[0] *s[10]*s[13] - s[8] *s[1]*s[14]
        + s[8]*s[2] *s[13] + s[12]*s[1] *s[10] - s[12]*s[2]*s[9];

    inv[2]  =   s[1]*s[6]*s[15] - s[1] *s[7]*s[14] - s[5] *s[2]*s[15]
        + s[5]*s[3]*s[14] + s[13]*s[2]*s[7]  - s[13]*s[3]*s[6];
    inv[6]  = - s[0]*s[6]*s[15] + s[0] *s[7]*s[14] + s[4] *s[2]*s[15]
        - s[4]*s[3]*s[14] - s[12]*s[2]*s[7]  + s[12]*s[3]*s[6];
    inv[10] =   s[0]*s[5]*s[15] - s[0] *s[7]*s[13] - s[4] *s[1]*s[15]
        + s[4]*s[3]*s[13] + s[12]*s[1]*s[7]  - s[12]*s[3]*s[5];
    inv[14] = - s[0]*s[5]*s[14] + s[0] *s[6]*s[13] + s[4] *s[1]*s[14]
        - s[4]*s[2]*s[13] - s[12]*s[1]*s[6]  + s[12]*s[2]*s[5];

    inv[3]  = - s[1]*s[6]*s[11] + s[1]*s[7]*s[10] + s[5]*s[2]*s[11]
        - s[5]*s[3]*s[10] - s[9]*s[2]*s[7]  + s[9]*s[3]*s[6];
    inv[7]  =   s[0]*s[6]*s[11] - s[0]*s[7]*s[10] - s[4]*s[2]*s[11]
        + s[4]*s[3]*s[10] + s[8]*s[2]*s[7]  - s[8]*s[3]*s[6];
    inv[11] = - s[0]*s[5]*s[11] + s[0]*s[7]*s[9]  + s[4]*s[1]*s[11]
        - s[4]*s[3]*s[9]  - s[8]*s[1]*s[7]  + s[8]*s[3]*s[5];
    inv[15] =   s[0]*s[5]*s[10] - s[0]*s[6]*s[9]  - s[4]*s[1]*s[10]
        + s[4]*s[2]*s[9]  + s[8]*s[1]*s[6]  - s[8]*s[2]*s[5];

    det = s[0]*inv[0] + s[1]*inv[4] + s[2]*inv[8] + s[3]*inv[12];
    if (det === 0) {
        return this;
    }

    det = 1 / det;
    for (i = 0; i < 16; i++) {
        d[i] = inv[i] * det;
    }

    return this;
};

/**
 * Calculate the inverse matrix of this, and set to this.
 * @return this
 */
Matrix4.prototype.invert = function() {
    return this.setInverseOf(this);
};

/**
 * Set the orthographic projection matrix.
 * @param left The coordinate of the left of clipping plane.
 * @param right The coordinate of the right of clipping plane.
 * @param bottom The coordinate of the bottom of clipping plane.
 * @param top The coordinate of the top top clipping plane.
 * @param near The distances to the nearer depth clipping plane. This value is minus if the plane is to be behind the viewer.
 * @param far The distances to the farther depth clipping plane. This value is minus if the plane is to be behind the viewer.
 * @return this
 */
Matrix4.prototype.setOrtho = function(left, right, bottom, top, near, far) {
    var e, rw, rh, rd;

    if (left === right || bottom === top || near === far) {
        throw 'null frustum';
    }

    rw = 1 / (right - left);
    rh = 1 / (top - bottom);
    rd = 1 / (far - near);

    e = this.elements;

    e[0]  = 2 * rw;
    e[1]  = 0;
    e[2]  = 0;
    e[3]  = 0;

    e[4]  = 0;
    e[5]  = 2 * rh;
    e[6]  = 0;
    e[7]  = 0;

    e[8]  = 0;
    e[9]  = 0;
    e[10] = -2 * rd;
    e[11] = 0;

    e[12] = -(right + left) * rw;
    e[13] = -(top + bottom) * rh;
    e[14] = -(far + near) * rd;
    e[15] = 1;

    return this;
};

/**
 * Multiply the orthographic projection matrix from the right.
 * @param left The coordinate of the left of clipping plane.
 * @param right The coordinate of the right of clipping plane.
 * @param bottom The coordinate of the bottom of clipping plane.
 * @param top The coordinate of the top top clipping plane.
 * @param near The distances to the nearer depth clipping plane. This value is minus if the plane is to be behind the viewer.
 * @param far The distances to the farther depth clipping plane. This value is minus if the plane is to be behind the viewer.
 * @return this
 */
Matrix4.prototype.ortho = function(left, right, bottom, top, near, far) {
    return this.concat(new Matrix4().setOrtho(left, right, bottom, top, near, far));
};

/**
 * Set the perspective projection matrix.
 * @param left The coordinate of the left of clipping plane.
 * @param right The coordinate of the right of clipping plane.
 * @param bottom The coordinate of the bottom of clipping plane.
 * @param top The coordinate of the top top clipping plane.
 * @param near The distances to the nearer depth clipping plane. This value must be plus value.
 * @param far The distances to the farther depth clipping plane. This value must be plus value.
 * @return this
 */
Matrix4.prototype.setFrustum = function(left, right, bottom, top, near, far) {
    var e, rw, rh, rd;

    if (left === right || top === bottom || near === far) {
        throw 'null frustum';
    }
    if (near <= 0) {
        throw 'near <= 0';
    }
    if (far <= 0) {
        throw 'far <= 0';
    }

    rw = 1 / (right - left);
    rh = 1 / (top - bottom);
    rd = 1 / (far - near);

    e = this.elements;

    e[ 0] = 2 * near * rw;
    e[ 1] = 0;
    e[ 2] = 0;
    e[ 3] = 0;

    e[ 4] = 0;
    e[ 5] = 2 * near * rh;
    e[ 6] = 0;
    e[ 7] = 0;

    e[ 8] = (right + left) * rw;
    e[ 9] = (top + bottom) * rh;
    e[10] = -(far + near) * rd;
    e[11] = -1;

    e[12] = 0;
    e[13] = 0;
    e[14] = -2 * near * far * rd;
    e[15] = 0;

    return this;
};

/**
 * Multiply the perspective projection matrix from the right.
 * @param left The coordinate of the left of clipping plane.
 * @param right The coordinate of the right of clipping plane.
 * @param bottom The coordinate of the bottom of clipping plane.
 * @param top The coordinate of the top top clipping plane.
 * @param near The distances to the nearer depth clipping plane. This value must be plus value.
 * @param far The distances to the farther depth clipping plane. This value must be plus value.
 * @return this
 */
Matrix4.prototype.frustum = function(left, right, bottom, top, near, far) {
    return this.concat(new Matrix4().setFrustum(left, right, bottom, top, near, far));
};

/**
 * Set the perspective projection matrix by fovy and aspect.
 * @param fovy The angle between the upper and lower sides of the frustum.
 * @param aspect The aspect ratio of the frustum. (width/height)
 * @param near The distances to the nearer depth clipping plane. This value must be plus value.
 * @param far The distances to the farther depth clipping plane. This value must be plus value.
 * @return this
 */
Matrix4.prototype.setPerspective = function(fovy, aspect, near, far) {
    var e, rd, s, ct;

    if (near === far || aspect === 0) {
        throw 'null frustum';
    }
    if (near <= 0) {
        throw 'near <= 0';
    }
    if (far <= 0) {
        throw 'far <= 0';
    }

    fovy = Math.PI * fovy / 180 / 2;
    s = Math.sin(fovy);
    if (s === 0) {
        throw 'null frustum';
    }

    rd = 1 / (far - near);
    ct = Math.cos(fovy) / s;

    e = this.elements;

    e[0]  = ct / aspect;
    e[1]  = 0;
    e[2]  = 0;
    e[3]  = 0;

    e[4]  = 0;
    e[5]  = ct;
    e[6]  = 0;
    e[7]  = 0;

    e[8]  = 0;
    e[9]  = 0;
    e[10] = -(far + near) * rd;
    e[11] = -1;

    e[12] = 0;
    e[13] = 0;
    e[14] = -2 * near * far * rd;
    e[15] = 0;

    return this;
};

/**
 * Multiply the perspective projection matrix from the right.
 * @param fovy The angle between the upper and lower sides of the frustum.
 * @param aspect The aspect ratio of the frustum. (width/height)
 * @param near The distances to the nearer depth clipping plane. This value must be plus value.
 * @param far The distances to the farther depth clipping plane. This value must be plus value.
 * @return this
 */
Matrix4.prototype.perspective = function(fovy, aspect, near, far) {
    return this.concat(new Matrix4().setPerspective(fovy, aspect, near, far));
};

/**
 * Set the matrix for scaling.
 * @param x The scale factor along the X axis
 * @param y The scale factor along the Y axis
 * @param z The scale factor along the Z axis
 * @return this
 */
Matrix4.prototype.setScale = function(x, y, z) {
    var e = this.elements;
    e[0] = x;  e[4] = 0;  e[8]  = 0;  e[12] = 0;
    e[1] = 0;  e[5] = y;  e[9]  = 0;  e[13] = 0;
    e[2] = 0;  e[6] = 0;  e[10] = z;  e[14] = 0;
    e[3] = 0;  e[7] = 0;  e[11] = 0;  e[15] = 1;
    return this;
};

/**
 * Multiply the matrix for scaling from the right.
 * @param x The scale factor along the X axis
 * @param y The scale factor along the Y axis
 * @param z The scale factor along the Z axis
 * @return this
 */
Matrix4.prototype.scale = function(x, y, z) {
    var e = this.elements;
    e[0] *= x;  e[4] *= y;  e[8]  *= z;
    e[1] *= x;  e[5] *= y;  e[9]  *= z;
    e[2] *= x;  e[6] *= y;  e[10] *= z;
    e[3] *= x;  e[7] *= y;  e[11] *= z;
    return this;
};

/**
 * Set the matrix for translation.
 * @param x The X value of a translation.
 * @param y The Y value of a translation.
 * @param z The Z value of a translation.
 * @return this
 */
Matrix4.prototype.setTranslate = function(x, y, z) {
    var e = this.elements;
    e[0] = 1;  e[4] = 0;  e[8]  = 0;  e[12] = x;
    e[1] = 0;  e[5] = 1;  e[9]  = 0;  e[13] = y;
    e[2] = 0;  e[6] = 0;  e[10] = 1;  e[14] = z;
    e[3] = 0;  e[7] = 0;  e[11] = 0;  e[15] = 1;
    return this;
};

/**
 * Multiply the matrix for translation from the right.
 * @param x The X value of a translation.
 * @param y The Y value of a translation.
 * @param z The Z value of a translation.
 * @return this
 */
Matrix4.prototype.translate = function(x, y, z) {
    var e = this.elements;
    e[12] += e[0] * x + e[4] * y + e[8]  * z;
    e[13] += e[1] * x + e[5] * y + e[9]  * z;
    e[14] += e[2] * x + e[6] * y + e[10] * z;
    e[15] += e[3] * x + e[7] * y + e[11] * z;
    return this;
};

/**
 * Set the matrix for rotation.
 * The vector of rotation axis may not be normalized.
 * @param angle The angle of rotation (degrees)
 * @param x The X coordinate of vector of rotation axis.
 * @param y The Y coordinate of vector of rotation axis.
 * @param z The Z coordinate of vector of rotation axis.
 * @return this
 */
Matrix4.prototype.setRotate = function(angle, x, y, z) {
    var e, s, c, len, rlen, nc, xy, yz, zx, xs, ys, zs;

    angle = Math.PI * angle / 180;
    e = this.elements;

    s = Math.sin(angle);
    c = Math.cos(angle);

    if (0 !== x && 0 === y && 0 === z) {
        // Rotation around X axis
        if (x < 0) {
            s = -s;
        }
        e[0] = 1;  e[4] = 0;  e[ 8] = 0;  e[12] = 0;
        e[1] = 0;  e[5] = c;  e[ 9] =-s;  e[13] = 0;
        e[2] = 0;  e[6] = s;  e[10] = c;  e[14] = 0;
        e[3] = 0;  e[7] = 0;  e[11] = 0;  e[15] = 1;
    } else if (0 === x && 0 !== y && 0 === z) {
        // Rotation around Y axis
        if (y < 0) {
            s = -s;
        }
        e[0] = c;  e[4] = 0;  e[ 8] = s;  e[12] = 0;
        e[1] = 0;  e[5] = 1;  e[ 9] = 0;  e[13] = 0;
        e[2] =-s;  e[6] = 0;  e[10] = c;  e[14] = 0;
        e[3] = 0;  e[7] = 0;  e[11] = 0;  e[15] = 1;
    } else if (0 === x && 0 === y && 0 !== z) {
        // Rotation around Z axis
        if (z < 0) {
            s = -s;
        }
        e[0] = c;  e[4] =-s;  e[ 8] = 0;  e[12] = 0;
        e[1] = s;  e[5] = c;  e[ 9] = 0;  e[13] = 0;
        e[2] = 0;  e[6] = 0;  e[10] = 1;  e[14] = 0;
        e[3] = 0;  e[7] = 0;  e[11] = 0;  e[15] = 1;
    } else {
        // Rotation around another axis
        len = Math.sqrt(x*x + y*y + z*z);
        if (len !== 1) {
            rlen = 1 / len;
            x *= rlen;
            y *= rlen;
            z *= rlen;
        }
        nc = 1 - c;
        xy = x * y;
        yz = y * z;
        zx = z * x;
        xs = x * s;
        ys = y * s;
        zs = z * s;

        e[ 0] = x*x*nc +  c;
        e[ 1] = xy *nc + zs;
        e[ 2] = zx *nc - ys;
        e[ 3] = 0;

        e[ 4] = xy *nc - zs;
        e[ 5] = y*y*nc +  c;
        e[ 6] = yz *nc + xs;
        e[ 7] = 0;

        e[ 8] = zx *nc + ys;
        e[ 9] = yz *nc - xs;
        e[10] = z*z*nc +  c;
        e[11] = 0;

        e[12] = 0;
        e[13] = 0;
        e[14] = 0;
        e[15] = 1;
    }

    return this;
};

/**
 * Multiply the matrix for rotation from the right.
 * The vector of rotation axis may not be normalized.
 * @param angle The angle of rotation (degrees)
 * @param x The X coordinate of vector of rotation axis.
 * @param y The Y coordinate of vector of rotation axis.
 * @param z The Z coordinate of vector of rotation axis.
 * @return this
 */
Matrix4.prototype.rotate = function(angle, x, y, z) {
    return this.concat(new Matrix4().setRotate(angle, x, y, z));
};

/**
 * Set the viewing matrix.
 * @param eyeX, eyeY, eyeZ The position of the eye point.
 * @param centerX, centerY, centerZ The position of the reference point.
 * @param upX, upY, upZ The direction of the up vector.
 * @return this
 */
Matrix4.prototype.setLookAt = function(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) {
    var e, fx, fy, fz, rlf, sx, sy, sz, rls, ux, uy, uz;

    fx = centerX - eyeX;
    fy = centerY - eyeY;
    fz = centerZ - eyeZ;

    // Normalize f.
    rlf = 1 / Math.sqrt(fx*fx + fy*fy + fz*fz);
    fx *= rlf;
    fy *= rlf;
    fz *= rlf;

    // Calculate cross product of f and up.
    sx = fy * upZ - fz * upY;
    sy = fz * upX - fx * upZ;
    sz = fx * upY - fy * upX;

    // Normalize s.
    rls = 1 / Math.sqrt(sx*sx + sy*sy + sz*sz);
    sx *= rls;
    sy *= rls;
    sz *= rls;

    // Calculate cross product of s and f.
    ux = sy * fz - sz * fy;
    uy = sz * fx - sx * fz;
    uz = sx * fy - sy * fx;

    // Set to this.
    e = this.elements;
    e[0] = sx;
    e[1] = ux;
    e[2] = -fx;
    e[3] = 0;

    e[4] = sy;
    e[5] = uy;
    e[6] = -fy;
    e[7] = 0;

    e[8] = sz;
    e[9] = uz;
    e[10] = -fz;
    e[11] = 0;

    e[12] = 0;
    e[13] = 0;
    e[14] = 0;
    e[15] = 1;

    // Translate.
    return this.translate(-eyeX, -eyeY, -eyeZ);
};

/**
 * Multiply the viewing matrix from the right.
 * @param eyeX, eyeY, eyeZ The position of the eye point.
 * @param centerX, centerY, centerZ The position of the reference point.
 * @param upX, upY, upZ The direction of the up vector.
 * @return this
 */
Matrix4.prototype.lookAt = function(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) {
    return this.concat(new Matrix4().setLookAt(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ));
};

/**
 * Multiply the matrix for project vertex to plane from the right.
 * @param plane The array[A, B, C, D] of the equation of plane "Ax + By + Cz + D = 0".
 * @param light The array which stored coordinates of the light. if light[3]=0, treated as parallel light.
 * @return this
 */
Matrix4.prototype.dropShadow = function(plane, light) {
    var mat = new Matrix4();
    var e = mat.elements;

    var dot = plane[0] * light[0] + plane[1] * light[1] + plane[2] * light[2] + plane[3] * light[3];

    e[ 0] = dot - light[0] * plane[0];
    e[ 1] =     - light[1] * plane[0];
    e[ 2] =     - light[2] * plane[0];
    e[ 3] =     - light[3] * plane[0];

    e[ 4] =     - light[0] * plane[1];
    e[ 5] = dot - light[1] * plane[1];
    e[ 6] =     - light[2] * plane[1];
    e[ 7] =     - light[3] * plane[1];

    e[ 8] =     - light[0] * plane[2];
    e[ 9] =     - light[1] * plane[2];
    e[10] = dot - light[2] * plane[2];
    e[11] =     - light[3] * plane[2];

    e[12] =     - light[0] * plane[3];
    e[13] =     - light[1] * plane[3];
    e[14] =     - light[2] * plane[3];
    e[15] = dot - light[3] * plane[3];

    return this.concat(mat);
}

/**
 * Multiply the matrix for project vertex to plane from the right.(Projected by parallel light.)
 * @param normX, normY, normZ The normal vector of the plane.(Not necessary to be normalized.)
 * @param planeX, planeY, planeZ The coordinate of arbitrary points on a plane.
 * @param lightX, lightY, lightZ The vector of the direction of light.(Not necessary to be normalized.)
 * @return this
 */
Matrix4.prototype.dropShadowDirectionally = function(normX, normY, normZ, planeX, planeY, planeZ, lightX, lightY, lightZ) {
    var a = planeX * normX + planeY * normY + planeZ * normZ;
    return this.dropShadow([normX, normY, normZ, -a], [lightX, lightY, lightZ, 0]);
};

/**
 * Constructor of Vector3
 * If opt_src is specified, new vector is initialized by opt_src.
 * @param opt_src source vector(option)
 */
var Vector3 = function(opt_src) {
    var v = new Float32Array(3);
    if (opt_src && typeof opt_src === 'object') {
        v[0] = opt_src[0]; v[1] = opt_src[1]; v[2] = opt_src[2];
    }
    this.elements = v;
}

/**
 * Normalize.
 * @return this
 */
Vector3.prototype.normalize = function() {
    var v = this.elements;
    var c = v[0], d = v[1], e = v[2], g = Math.sqrt(c*c+d*d+e*e);
    if(g){
        if(g == 1)
            return this;
    } else {
        v[0] = 0; v[1] = 0; v[2] = 0;
        return this;
    }
    g = 1/g;
    v[0] = c*g; v[1] = d*g; v[2] = e*g;
    return this;
};

/**
 * Constructor of Vector4
 * If opt_src is specified, new vector is initialized by opt_src.
 * @param opt_src source vector(option)
 */
var Vector4 = function(opt_src) {
    var v = new Float32Array(4);
    if (opt_src && typeof opt_src === 'object') {
        v[0] = opt_src[0]; v[1] = opt_src[1]; v[2] = opt_src[2]; v[3] = opt_src[3];
    }
    this.elements = v;
}
function initShaders(gl, vshader, fshader) {
    var program = createProgram(gl, vshader, fshader);
    if (!program) {
        console.log('Failed to create program');
        return false;
    }

    gl.useProgram(program);
    gl.program = program;

    return true;
}

/**
 * Create the linked program object
 * @param gl GL context
 * @param vshader a vertex shader program (string)
 * @param fshader a fragment shader program (string)
 * @return created program object, or null if the creation has failed
 */
function createProgram(gl, vshader, fshader) {
    // Create shader object
    var vertexShader = loadShader(gl, gl.VERTEX_SHADER, vshader);
    var fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fshader);
    if (!vertexShader || !fragmentShader) {
        return null;
    }

    // Create a program object
    var program = gl.createProgram();
    if (!program) {
        return null;
    }

    // Attach the shader objects
    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);

    // Link the program object
    gl.linkProgram(program);

    // Check the result of linking
    var linked = gl.getProgramParameter(program, gl.LINK_STATUS);
    if (!linked) {
        var error = gl.getProgramInfoLog(program);
        console.log('Failed to link program: ' + error);
        gl.deleteProgram(program);
        gl.deleteShader(fragmentShader);
        gl.deleteShader(vertexShader);
        return null;
    }
    return program;
}

/**
 * Create a shader object
 * @param gl GL context
 * @param type the type of the shader object to be created
 * @param source shader program (string)
 * @return created shader object, or null if the creation has failed.
 */
function loadShader(gl, type, source) {
    // Create shader object
    var shader = gl.createShader(type);
    if (shader == null) {
        console.log('unable to create shader');
        return null;
    }

    // Set the shader program
    gl.shaderSource(shader, source);

    // Compile the shader
    gl.compileShader(shader);

    // Check the result of compilation
    var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
    if (!compiled) {
        var error = gl.getShaderInfoLog(shader);
        console.log('Failed to compile shader: ' + error);
        gl.deleteShader(shader);
        return null;
    }

    return shader;
}

/**
 * Initialize and get the rendering for WebGL
 * @param canvas <cavnas> element
 * @param opt_debug flag to initialize the context for debugging
 * @return the rendering context for WebGL
 */
function getWebGLContext(canvas, opt_debug) {
    // Get the rendering context for WebGL
    var gl = WebGLUtils.setupWebGL(canvas);
    if (!gl) return null;

    // if opt_debug is explicitly false, create the context for debugging
    if (arguments.length < 2 || opt_debug) {
        gl = WebGLDebugUtils.makeDebugContext(gl);
    }

    return gl;
}

// Various functions for helping debug WebGL apps.

WebGLDebugUtils = function() {

    /**
     * Wrapped logging function.
     * @param {string} msg Message to log.
     */
    var log = function(msg) {
        if (window.console && window.console.log) {
            window.console.log(msg);
        }
    };

    /**
     * Which arguements are enums.
     * @type {!Object.<number, string>}
     */
    var glValidEnumContexts = {

        // Generic setters and getters

        'enable': { 0:true },
        'disable': { 0:true },
        'getParameter': { 0:true },

        // Rendering

        'drawArrays': { 0:true },
        'drawElements': { 0:true, 2:true },

        // Shaders

        'createShader': { 0:true },
        'getShaderParameter': { 1:true },
        'getProgramParameter': { 1:true },

        // Vertex attributes

        'getVertexAttrib': { 1:true },
        'vertexAttribPointer': { 2:true },

        // Textures

        'bindTexture': { 0:true },
        'activeTexture': { 0:true },
        'getTexParameter': { 0:true, 1:true },
        'texParameterf': { 0:true, 1:true },
        'texParameteri': { 0:true, 1:true, 2:true },
        'texImage2D': { 0:true, 2:true, 6:true, 7:true },
        'texSubImage2D': { 0:true, 6:true, 7:true },
        'copyTexImage2D': { 0:true, 2:true },
        'copyTexSubImage2D': { 0:true },
        'generateMipmap': { 0:true },

        // Buffer objects

        'bindBuffer': { 0:true },
        'bufferData': { 0:true, 2:true },
        'bufferSubData': { 0:true },
        'getBufferParameter': { 0:true, 1:true },

        // Renderbuffers and framebuffers

        'pixelStorei': { 0:true, 1:true },
        'readPixels': { 4:true, 5:true },
        'bindRenderbuffer': { 0:true },
        'bindFramebuffer': { 0:true },
        'checkFramebufferStatus': { 0:true },
        'framebufferRenderbuffer': { 0:true, 1:true, 2:true },
        'framebufferTexture2D': { 0:true, 1:true, 2:true },
        'getFramebufferAttachmentParameter': { 0:true, 1:true, 2:true },
        'getRenderbufferParameter': { 0:true, 1:true },
        'renderbufferStorage': { 0:true, 1:true },

        // Frame buffer operations (clear, blend, depth test, stencil)

        'clear': { 0:true },
        'depthFunc': { 0:true },
        'blendFunc': { 0:true, 1:true },
        'blendFuncSeparate': { 0:true, 1:true, 2:true, 3:true },
        'blendEquation': { 0:true },
        'blendEquationSeparate': { 0:true, 1:true },
        'stencilFunc': { 0:true },
        'stencilFuncSeparate': { 0:true, 1:true },
        'stencilMaskSeparate': { 0:true },
        'stencilOp': { 0:true, 1:true, 2:true },
        'stencilOpSeparate': { 0:true, 1:true, 2:true, 3:true },

        // Culling

        'cullFace': { 0:true },
        'frontFace': { 0:true },
    };

    /**
     * Map of numbers to names.
     * @type {Object}
     */
    var glEnums = null;

    /**
     * Initializes this module. Safe to call more than once.
     * @param {!WebGLRenderingContext} ctx A WebGL context. If
     *    you have more than one context it doesn't matter which one
     *    you pass in, it is only used to pull out constants.
     */
    function init(ctx) {
        if (glEnums == null) {
            glEnums = { };
            for (var propertyName in ctx) {
                if (typeof ctx[propertyName] == 'number') {
                    glEnums[ctx[propertyName]] = propertyName;
                }
            }
        }
    }

    /**
     * Checks the utils have been initialized.
     */
    function checkInit() {
        if (glEnums == null) {
            throw 'WebGLDebugUtils.init(ctx) not called';
        }
    }

    /**
     * Returns true or false if value matches any WebGL enum
     * @param {*} value Value to check if it might be an enum.
     * @return {boolean} True if value matches one of the WebGL defined enums
     */
    function mightBeEnum(value) {
        checkInit();
        return (glEnums[value] !== undefined);
    }

    /**
     * Gets an string version of an WebGL enum.
     *
     * Example:
     *   var str = WebGLDebugUtil.glEnumToString(ctx.getError());
     *
     * @param {number} value Value to return an enum for
     * @return {string} The string version of the enum.
     */
    function glEnumToString(value) {
        checkInit();
        var name = glEnums[value];
        return (name !== undefined) ? name :
            ("*UNKNOWN WebGL ENUM (0x" + value.toString(16) + ")");
    }

    /**
     * Returns the string version of a WebGL argument.
     * Attempts to convert enum arguments to strings.
     * @param {string} functionName the name of the WebGL function.
     * @param {number} argumentIndx the index of the argument.
     * @param {*} value The value of the argument.
     * @return {string} The value as a string.
     */
    function glFunctionArgToString(functionName, argumentIndex, value) {
        var funcInfo = glValidEnumContexts[functionName];
        if (funcInfo !== undefined) {
            if (funcInfo[argumentIndex]) {
                return glEnumToString(value);
            }
        }
        return value.toString();
    }

    /**
     * Given a WebGL context returns a wrapped context that calls
     * gl.getError after every command and calls a function if the
     * result is not gl.NO_ERROR.
     *
     * @param {!WebGLRenderingContext} ctx The webgl context to
     *        wrap.
     * @param {!function(err, funcName, args): void} opt_onErrorFunc
     *        The function to call when gl.getError returns an
     *        error. If not specified the default function calls
     *        console.log with a message.
     */
    function makeDebugContext(ctx, opt_onErrorFunc) {
        init(ctx);
        opt_onErrorFunc = opt_onErrorFunc || function(err, functionName, args) {
                // apparently we can't do args.join(",");
                var argStr = "";
                for (var ii = 0; ii < args.length; ++ii) {
                    argStr += ((ii == 0) ? '' : ', ') +
                        glFunctionArgToString(functionName, ii, args[ii]);
                }
                log("WebGL error "+ glEnumToString(err) + " in "+ functionName +
                    "(" + argStr + ")");
            };

        // Holds booleans for each GL error so after we get the error ourselves
        // we can still return it to the client app.
        var glErrorShadow = { };

        // Makes a function that calls a WebGL function and then calls getError.
        function makeErrorWrapper(ctx, functionName) {
            return function() {
                var result = ctx[functionName].apply(ctx, arguments);
                var err = ctx.getError();
                if (err != 0) {
                    glErrorShadow[err] = true;
                    opt_onErrorFunc(err, functionName, arguments);
                }
                return result;
            };
        }

        // Make a an object that has a copy of every property of the WebGL context
        // but wraps all functions.
        var wrapper = {};
        for (var propertyName in ctx) {
            if (typeof ctx[propertyName] == 'function') {
                wrapper[propertyName] = makeErrorWrapper(ctx, propertyName);
            } else {
                wrapper[propertyName] = ctx[propertyName];
            }
        }

        // Override the getError function with one that returns our saved results.
        wrapper.getError = function() {
            for (var err in glErrorShadow) {
                if (glErrorShadow[err]) {
                    glErrorShadow[err] = false;
                    return err;
                }
            }
            return ctx.NO_ERROR;
        };

        return wrapper;
    }

    function resetToInitialState(ctx) {
        var numAttribs = ctx.getParameter(ctx.MAX_VERTEX_ATTRIBS);
        var tmp = ctx.createBuffer();
        ctx.bindBuffer(ctx.ARRAY_BUFFER, tmp);
        for (var ii = 0; ii < numAttribs; ++ii) {
            ctx.disableVertexAttribArray(ii);
            ctx.vertexAttribPointer(ii, 4, ctx.FLOAT, false, 0, 0);
            ctx.vertexAttrib1f(ii, 0);
        }
        ctx.deleteBuffer(tmp);

        var numTextureUnits = ctx.getParameter(ctx.MAX_TEXTURE_IMAGE_UNITS);
        for (var ii = 0; ii < numTextureUnits; ++ii) {
            ctx.activeTexture(ctx.TEXTURE0 + ii);
            ctx.bindTexture(ctx.TEXTURE_CUBE_MAP, null);
            ctx.bindTexture(ctx.TEXTURE_2D, null);
        }

        ctx.activeTexture(ctx.TEXTURE0);
        ctx.useProgram(null);
        ctx.bindBuffer(ctx.ARRAY_BUFFER, null);
        ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, null);
        ctx.bindFramebuffer(ctx.FRAMEBUFFER, null);
        ctx.bindRenderbuffer(ctx.RENDERBUFFER, null);
        ctx.disable(ctx.BLEND);
        ctx.disable(ctx.CULL_FACE);
        ctx.disable(ctx.DEPTH_TEST);
        ctx.disable(ctx.DITHER);
        ctx.disable(ctx.SCISSOR_TEST);
        ctx.blendColor(0, 0, 0, 0);
        ctx.blendEquation(ctx.FUNC_ADD);
        ctx.blendFunc(ctx.ONE, ctx.ZERO);
        ctx.clearColor(0, 0, 0, 0);
        ctx.clearDepth(1);
        ctx.clearStencil(-1);
        ctx.colorMask(true, true, true, true);
        ctx.cullFace(ctx.BACK);
        ctx.depthFunc(ctx.LESS);
        ctx.depthMask(true);
        ctx.depthRange(0, 1);
        ctx.frontFace(ctx.CCW);
        ctx.hint(ctx.GENERATE_MIPMAP_HINT, ctx.DONT_CARE);
        ctx.lineWidth(1);
        ctx.pixelStorei(ctx.PACK_ALIGNMENT, 4);
        ctx.pixelStorei(ctx.UNPACK_ALIGNMENT, 4);
        ctx.pixelStorei(ctx.UNPACK_FLIP_Y_WEBGL, false);
        ctx.pixelStorei(ctx.UNPACK_PREMULTIPLY_ALPHA_WEBGL, false);
        // TODO: Delete this IF.
        if (ctx.UNPACK_COLORSPACE_CONVERSION_WEBGL) {
            ctx.pixelStorei(ctx.UNPACK_COLORSPACE_CONVERSION_WEBGL, ctx.BROWSER_DEFAULT_WEBGL);
        }
        ctx.polygonOffset(0, 0);
        ctx.sampleCoverage(1, false);
        ctx.scissor(0, 0, ctx.canvas.width, ctx.canvas.height);
        ctx.stencilFunc(ctx.ALWAYS, 0, 0xFFFFFFFF);
        ctx.stencilMask(0xFFFFFFFF);
        ctx.stencilOp(ctx.KEEP, ctx.KEEP, ctx.KEEP);
        ctx.viewport(0, 0, ctx.canvas.clientWidth, ctx.canvas.clientHeight);
        ctx.clear(ctx.COLOR_BUFFER_BIT | ctx.DEPTH_BUFFER_BIT | ctx.STENCIL_BUFFER_BIT);

        // TODO: This should NOT be needed but Firefox fails with 'hint'
        while(ctx.getError());
    }

    function makeLostContextSimulatingContext(ctx) {
        var wrapper_ = {};
        var contextId_ = 1;
        var contextLost_ = false;
        var resourceId_ = 0;
        var resourceDb_ = [];
        var onLost_ = undefined;
        var onRestored_ = undefined;
        var nextOnRestored_ = undefined;

        // Holds booleans for each GL error so can simulate errors.
        var glErrorShadow_ = { };

        function isWebGLObject(obj) {
            //return false;
            return (obj instanceof WebGLBuffer ||
            obj instanceof WebGLFramebuffer ||
            obj instanceof WebGLProgram ||
            obj instanceof WebGLRenderbuffer ||
            obj instanceof WebGLShader ||
            obj instanceof WebGLTexture);
        }

        function checkResources(args) {
            for (var ii = 0; ii < args.length; ++ii) {
                var arg = args[ii];
                if (isWebGLObject(arg)) {
                    return arg.__webglDebugContextLostId__ == contextId_;
                }
            }
            return true;
        }

        function clearErrors() {
            var k = Object.keys(glErrorShadow_);
            for (var ii = 0; ii < k.length; ++ii) {
                delete glErrorShdow_[k];
            }
        }

        // Makes a function that simulates WebGL when out of context.
        function makeLostContextWrapper(ctx, functionName) {
            var f = ctx[functionName];
            return function() {
                // Only call the functions if the context is not lost.
                if (!contextLost_) {
                    if (!checkResources(arguments)) {
                        glErrorShadow_[ctx.INVALID_OPERATION] = true;
                        return;
                    }
                    var result = f.apply(ctx, arguments);
                    return result;
                }
            };
        }

        for (var propertyName in ctx) {
            if (typeof ctx[propertyName] == 'function') {
                wrapper_[propertyName] = makeLostContextWrapper(ctx, propertyName);
            } else {
                wrapper_[propertyName] = ctx[propertyName];
            }
        }

        function makeWebGLContextEvent(statusMessage) {
            return {statusMessage: statusMessage};
        }

        function freeResources() {
            for (var ii = 0; ii < resourceDb_.length; ++ii) {
                var resource = resourceDb_[ii];
                if (resource instanceof WebGLBuffer) {
                    ctx.deleteBuffer(resource);
                } else if (resource instanceof WebctxFramebuffer) {
                    ctx.deleteFramebuffer(resource);
                } else if (resource instanceof WebctxProgram) {
                    ctx.deleteProgram(resource);
                } else if (resource instanceof WebctxRenderbuffer) {
                    ctx.deleteRenderbuffer(resource);
                } else if (resource instanceof WebctxShader) {
                    ctx.deleteShader(resource);
                } else if (resource instanceof WebctxTexture) {
                    ctx.deleteTexture(resource);
                }
            }
        }

        wrapper_.loseContext = function() {
            if (!contextLost_) {
                contextLost_ = true;
                ++contextId_;
                while (ctx.getError());
                clearErrors();
                glErrorShadow_[ctx.CONTEXT_LOST_WEBGL] = true;
                setTimeout(function() {
                    if (onLost_) {
                        onLost_(makeWebGLContextEvent("context lost"));
                    }
                }, 0);
            }
        };

        wrapper_.restoreContext = function() {
            if (contextLost_) {
                if (onRestored_) {
                    setTimeout(function() {
                        freeResources();
                        resetToInitialState(ctx);
                        contextLost_ = false;
                        if (onRestored_) {
                            var callback = onRestored_;
                            onRestored_ = nextOnRestored_;
                            nextOnRestored_ = undefined;
                            callback(makeWebGLContextEvent("context restored"));
                        }
                    }, 0);
                } else {
                    throw "You can not restore the context without a listener"
                }
            }
        };

        // Wrap a few functions specially.
        wrapper_.getError = function() {
            if (!contextLost_) {
                var err;
                while (err = ctx.getError()) {
                    glErrorShadow_[err] = true;
                }
            }
            for (var err in glErrorShadow_) {
                if (glErrorShadow_[err]) {
                    delete glErrorShadow_[err];
                    return err;
                }
            }
            return ctx.NO_ERROR;
        };

        var creationFunctions = [
            "createBuffer",
            "createFramebuffer",
            "createProgram",
            "createRenderbuffer",
            "createShader",
            "createTexture"
        ];
        for (var ii = 0; ii < creationFunctions.length; ++ii) {
            var functionName = creationFunctions[ii];
            wrapper_[functionName] = function(f) {
                return function() {
                    if (contextLost_) {
                        return null;
                    }
                    var obj = f.apply(ctx, arguments);
                    obj.__webglDebugContextLostId__ = contextId_;
                    resourceDb_.push(obj);
                    return obj;
                };
            }(ctx[functionName]);
        }

        var functionsThatShouldReturnNull = [
            "getActiveAttrib",
            "getActiveUniform",
            "getBufferParameter",
            "getContextAttributes",
            "getAttachedShaders",
            "getFramebufferAttachmentParameter",
            "getParameter",
            "getProgramParameter",
            "getProgramInfoLog",
            "getRenderbufferParameter",
            "getShaderParameter",
            "getShaderInfoLog",
            "getShaderSource",
            "getTexParameter",
            "getUniform",
            "getUniformLocation",
            "getVertexAttrib"
        ];
        for (var ii = 0; ii < functionsThatShouldReturnNull.length; ++ii) {
            var functionName = functionsThatShouldReturnNull[ii];
            wrapper_[functionName] = function(f) {
                return function() {
                    if (contextLost_) {
                        return null;
                    }
                    return f.apply(ctx, arguments);
                }
            }(wrapper_[functionName]);
        }

        var isFunctions = [
            "isBuffer",
            "isEnabled",
            "isFramebuffer",
            "isProgram",
            "isRenderbuffer",
            "isShader",
            "isTexture"
        ];
        for (var ii = 0; ii < isFunctions.length; ++ii) {
            var functionName = isFunctions[ii];
            wrapper_[functionName] = function(f) {
                return function() {
                    if (contextLost_) {
                        return false;
                    }
                    return f.apply(ctx, arguments);
                }
            }(wrapper_[functionName]);
        }

        wrapper_.checkFramebufferStatus = function(f) {
            return function() {
                if (contextLost_) {
                    return ctx.FRAMEBUFFER_UNSUPPORTED;
                }
                return f.apply(ctx, arguments);
            };
        }(wrapper_.checkFramebufferStatus);

        wrapper_.getAttribLocation = function(f) {
            return function() {
                if (contextLost_) {
                    return -1;
                }
                return f.apply(ctx, arguments);
            };
        }(wrapper_.getAttribLocation);

        wrapper_.getVertexAttribOffset = function(f) {
            return function() {
                if (contextLost_) {
                    return 0;
                }
                return f.apply(ctx, arguments);
            };
        }(wrapper_.getVertexAttribOffset);

        wrapper_.isContextLost = function() {
            return contextLost_;
        };

        function wrapEvent(listener) {
            if (typeof(listener) == "function") {
                return listener;
            } else {
                return function(info) {
                    listener.handleEvent(info);
                }
            }
        }

        wrapper_.registerOnContextLostListener = function(listener) {
            onLost_ = wrapEvent(listener);
        };

        wrapper_.registerOnContextRestoredListener = function(listener) {
            if (contextLost_) {
                nextOnRestored_ = wrapEvent(listener);
            } else {
                onRestored_ = wrapEvent(listener);
            }
        }

        return wrapper_;
    }

    return {
        /**
         * Initializes this module. Safe to call more than once.
         * @param {!WebGLRenderingContext} ctx A WebGL context. If
         *    you have more than one context it doesn't matter which one
         *    you pass in, it is only used to pull out constants.
         */
        'init': init,

        /**
         * Returns true or false if value matches any WebGL enum
         * @param {*} value Value to check if it might be an enum.
         * @return {boolean} True if value matches one of the WebGL defined enums
         */
        'mightBeEnum': mightBeEnum,

        /**
         * Gets an string version of an WebGL enum.
         *
         * Example:
         *   WebGLDebugUtil.init(ctx);
         *   var str = WebGLDebugUtil.glEnumToString(ctx.getError());
         *
         * @param {number} value Value to return an enum for
         * @return {string} The string version of the enum.
         */
        'glEnumToString': glEnumToString,

        /**
         * Converts the argument of a WebGL function to a string.
         * Attempts to convert enum arguments to strings.
         *
         * Example:
         *   WebGLDebugUtil.init(ctx);
         *   var str = WebGLDebugUtil.glFunctionArgToString('bindTexture', 0, gl.TEXTURE_2D);
         *
         * would return 'TEXTURE_2D'
         *
         * @param {string} functionName the name of the WebGL function.
         * @param {number} argumentIndx the index of the argument.
         * @param {*} value The value of the argument.
         * @return {string} The value as a string.
         */
        'glFunctionArgToString': glFunctionArgToString,

        /**
         * Given a WebGL context returns a wrapped context that calls
         * gl.getError after every command and calls a function if the
         * result is not NO_ERROR.
         *
         * You can supply your own function if you want. For example, if you'd like
         * an exception thrown on any GL error you could do this
         *
         *    function throwOnGLError(err, funcName, args) {
   *      throw WebGLDebugUtils.glEnumToString(err) + " was caused by call to" +
   *            funcName;
   *    };
         *
         *    ctx = WebGLDebugUtils.makeDebugContext(
         *        canvas.getContext("webgl"), throwOnGLError);
         *
         * @param {!WebGLRenderingContext} ctx The webgl context to wrap.
         * @param {!function(err, funcName, args): void} opt_onErrorFunc The function
         *     to call when gl.getError returns an error. If not specified the default
         *     function calls console.log with a message.
         */
        'makeDebugContext': makeDebugContext,

        /**
         * Given a WebGL context returns a wrapped context that adds 4
         * functions.
         *
         * ctx.loseContext:
         *   simulates a lost context event.
         *
         * ctx.restoreContext:
         *   simulates the context being restored.
         *
         * ctx.registerOnContextLostListener(listener):
         *   lets you register a listener for context lost. Use instead
         *   of addEventListener('webglcontextlostevent', listener);
         *
         * ctx.registerOnContextRestoredListener(listener):
         *   lets you register a listener for context restored. Use
         *   instead of addEventListener('webglcontextrestored',
         *   listener);
         *
         * @param {!WebGLRenderingContext} ctx The webgl context to wrap.
         */
        'makeLostContextSimulatingContext': makeLostContextSimulatingContext,
        /**
         * Resets a context to the initial state.
         * @param {!WebGLRenderingContext} ctx The webgl context to
         *     reset.
         */
        'resetToInitialState': resetToInitialState
    };

}();
WebGLUtils = function() {

    /**
     * Creates the HTLM for a failure message
     * @param {string} canvasContainerId id of container of th
     *        canvas.
     * @return {string} The html.
     */
    var makeFailHTML = function(msg) {
        return '' +
            '<div style="margin: auto; width:500px;z-index:10000;margin-top:20em;text-align:center;">' + msg + '</div>';
        return '' +
            '<table style="background-color: #8CE; width: 100%; height: 100%;"><tr>' +
            '<td align="center">' +
            '<div style="display: table-cell; vertical-align: middle;">' +
            '<div style="">' + msg + '</div>' +
            '</div>' +
            '</td></tr></table>';
    };

    /**
     * Mesasge for getting a webgl browser
     * @type {string}
     */
    var GET_A_WEBGL_BROWSER = '' +
        'This page requires a browser that supports WebGL.<br/>' +
        '<a href="http://get.webgl.org">Click here to upgrade your browser.</a>';

    /**
     * Mesasge for need better hardware
     * @type {string}
     */
    var OTHER_PROBLEM = '' +
        "It doesn't appear your computer can support WebGL.<br/>" +
        '<a href="http://get.webgl.org">Click here for more information.</a>';

    /**
     * Creates a webgl context. If creation fails it will
     * change the contents of the container of the <canvas>
     * tag to an error message with the correct links for WebGL.
     * @param {Element} canvas. The canvas element to create a
     *     context from.
     * @param {WebGLContextCreationAttirbutes} opt_attribs Any
     *     creation attributes you want to pass in.
     * @param {function:(msg)} opt_onError An function to call
     *     if there is an error during creation.
     * @return {WebGLRenderingContext} The created context.
     */
    var setupWebGL = function(canvas, opt_attribs, opt_onError) {
        function handleCreationError(msg) {
            var container = document.getElementsByTagName("body")[0];
            //var container = canvas.parentNode;
            if (container) {
                var str = window.WebGLRenderingContext ?
                    OTHER_PROBLEM :
                    GET_A_WEBGL_BROWSER;
                if (msg) {
                    str += "<br/><br/>Status: " + msg;
                }
                container.innerHTML = makeFailHTML(str);
            }
        };

        opt_onError = opt_onError || handleCreationError;

        if (canvas.addEventListener) {
            canvas.addEventListener("webglcontextcreationerror", function(event) {
                opt_onError(event.statusMessage);
            }, false);
        }
        var context = create3DContext(canvas, opt_attribs);
        if (!context) {
            if (!window.WebGLRenderingContext) {
                opt_onError("");
            } else {
                opt_onError("");
            }
        }

        return context;
    };

    /**
     * Creates a webgl context.
     * @param {!Canvas} canvas The canvas tag to get context
     *     from. If one is not passed in one will be created.
     * @return {!WebGLContext} The created context.
     */
    var create3DContext = function(canvas, opt_attribs) {
        var names = ["webgl", "experimental-webgl", "webkit-3d", "moz-webgl"];
        var context = null;
        for (var ii = 0; ii < names.length; ++ii) {
            try {
                context = canvas.getContext(names[ii], opt_attribs);
            } catch(e) {}
            if (context) {
                break;
            }
        }
        return context;
    }

    return {
        create3DContext: create3DContext,
        setupWebGL: setupWebGL
    };
}();

/**
 * Provides requestAnimationFrame in a cross browser
 * way.
 */
if (!window.requestAnimationFrame) {
    window.requestAnimationFrame = (function() {
        return window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            window.mozRequestAnimationFrame ||
            window.oRequestAnimationFrame ||
            window.msRequestAnimationFrame ||
            function(/* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {
                window.setTimeout(callback, 1000/60);
            };
    })();
}

/** * ERRATA: 'cancelRequestAnimationFrame' renamed to 'cancelAnimationFrame' to reflect an update to the W3C Animation-Timing Spec.
 *
 * Cancels an animation frame request.
 * Checks for cross-browser support, falls back to clearTimeout.
 * @param {number}  Animation frame request. */
if (!window.cancelAnimationFrame) {
    window.cancelAnimationFrame = (window.cancelRequestAnimationFrame ||
    window.webkitCancelAnimationFrame || window.webkitCancelRequestAnimationFrame ||
    window.mozCancelAnimationFrame || window.mozCancelRequestAnimationFrame ||
    window.msCancelAnimationFrame || window.msCancelRequestAnimationFrame ||
    window.oCancelAnimationFrame || window.oCancelRequestAnimationFrame ||
    window.clearTimeout);
}